1. Field of the Invention
The present invention relates to feeding of a recording medium in printers. More specifically, the present invention relates to control of line feeding of a recording medium in conjunction with print head nozzle firing so as to advance the recording medium for high resolution printing with a lower amount of line feeding motor steps.
2. Description of the Related Art
Line feeding in printers refers to the advancement of a recording medium through the printer during printing operations. During printing operations, the recording medium is fed through the printer by line feed rollers that are driven by a line feed motor controlled by a controller. The line feed motor and the line feed rollers are connected by a drivetrain so that as the line feed motor rotates, the line feed rollers also rotate. The recording medium is fed between the line feed rollers and pinch rollers and as the line feed rollers rotate, the recording medium is fed through the printer.
One type of line feed motor is known as a stepper motor. A stepper motor rotates in steps, i.e. stepped increments or pulses. Each increment or pulse corresponds to a predetermined amount (or phase) of rotation. Some of the most common stepper motors used in printers have stepped increments of 1.8xc2x0 (corresponding to a 200 pulse motor where 200 pulsesxc3x971.8xc2x0=360xc2x0), 3.6xc2x0 (corresponding to a 100 pulse motor), and 3.75xc2x0 (corresponding to a 96 pulse motor). For each increment (pulse) that the line feed motor rotates, the line feed rollers also rotate and feed the recording medium a horizontal amount corresponding to the amount of rotation of the line feed rollers. The amount of rotation of the line feed rollers is determined by the drivetrain ratio employed between the line feed motor and the line feed rollers.
Conventionally, the drivetrain ratio has been set so that one pulse of the line feed motor advances the recording medium an amount equivalent to the maximum resolution of the printer. For example, where the maximum resolution of a printout of the printer is 600 dpi (dots per inch), the drivetrain ratio has been set so that one pulse of the line feed motor corresponds to a 600 dpi pitch line feed of the recording medium. Thus, the line feed ratio to obtain a 600 dpi resolution printout would be 1/600 (1 pulse equals 600 dpi advancement of the recording medium).
In order to obtain higher resolution printouts, such as a 1200 dpi printout, additional motor pulses are required. Consider, for example, a print head having 100 nozzles spaced at a 600 dpi pitch printing a 1200 dpi image. The print head performs two scans across the same scan area to perform 1200 dpi printing (a first scan printing at 600 dpi and a second scan also printing at 600 dpi after a 1200 dpi paper advancement). After the second scan, the paper is advanced to the end of the 100 nozzle printout. In order to advance the paper to the end of the 100 nozzle print, 200 pulses of the motor would be required (it takes 2 pulses to advance the paper one 600 dpi pixel, therefore it takes 200 pulses to advance the paper 100 pixels). The 200 pulses result in a slower line feed speed than would otherwise be required if less motor pulses were needed to advance the paper the same 100 pixel amount. Thus, what is needed is a way to increase the line feed speed at higher resolutions.
It has been proposed that, to increase the line feed speed, that the motor speed itself could be increased. However, higher resolution printouts also require a higher degree of accuracy of the motor. Faster and more accurate motors are expensive and increase the cost of the printer. Therefore, what is needed is a way to increase the line feed speed at higher resolutions and to maintain accuracy without a significant increase in the motor cost.
The present invention addresses the foregoing by feeding the recording medium a fractional amount greater than the maximum resolution of the printer for each increment (phase) of the line feed motor and controlling a number of nozzles that eject ink based on the number of increments. In one representative embodiment, each increment of the line feed motor results in a 1.5 pixel advancement of the recording medium in a pixel resolution of a print head. A comparison of this embodiment to the above described example in which a 1/600 feeding ratio results, the present invention results in a 1/400 feeding ratio for the same motor. Therefore, less line feed motor increments are required to advance the recording medium an equivalent amount. Since less motor increments are required, the line feed speed is increased. Moreover, controlling the nozzle firing provides for adjustment of the nozzle firing for the fractional increments, thereby providing for printing a continuous image.
Thus, in one aspect the invention is printing images on a recording medium fed through a printer by actuating a line feeding motor in predetermined stepped increments, feeding the recording medium through the printer by a line feeding device driven by the line feeding motor, printing an image on the recording medium by a print head scanning across the recording medium and ejecting ink from nozzles, the print head having j nozzles spaced at a predetermined pixel resolution that is less than a pixel resolution printed by the printer, j being an integer number, controlling the line feed motor to actuate in stepped increments, and controlling a number of the j nozzles utilized in printing the image. For each stepped increment of the line feed motor, the line feeding device feeds the recording medium (mxc3x971/n) pixels of the print head pixel resolution, where m and n are integer numbers and m is greater than n. The j nozzles that print in any one scan of the print head are controlled based on the number of increments of the line feed motor.
In a related aspect, the invention is feeding a recording medium through a printer for printing images on the recording medium by actuating a line feeding motor in stepped increments, feeding the recording medium through the printer by a line feeding device driven by the line feeding motor, and performing banded printing of an image on the recording medium by a print head scanning across the recording medium, the print head having nozzles spaced at a first resolution. One increment of the line feeding motor results in a feed amount of m/n times the print head nozzle spacing, where m/n is greater than 1, and m and n are integer values where m is greater than n, and, to print the image, the line feeding motor is actuated n increments, or an integer multiple of n increments between bands.
In other aspects, m may be equal to 3 and n equal to 2. The number of increments of the line feed motor may equal 2 so that every 2 increments equals a line feed of 3 pixels in the pixel resolution printed by the printer. The number of nozzles, j, may equal 304 or 80, and 300 or less, or 78 or less nozzles may be utilized to print in any one scan of the print head. The j nozzles may be spaced at a 600 dpi resolution and the printed resolution of the printer may be 1200 dpi.
In another aspect, the invention processes image data to be sent to a printer by performing rasterization, color conversion and halftone processing on the image data, storing the processed image data in a print buffer for transmission to the printer, calculating a line skip amount, calculating a buffer offset amount, and adjusting a starting position for storing of the image data in the print buffer based on a result of the calculated buffer offset amount. The line skip amount and the buffer offset amount are calculated in a case where a first line of image data to be stored in the print buffer is white data. Additionally, the printer has a line feed ratio of mxc3x971/n in a pixel resolution of a print head, where m and n are integer numbers greater than 1, m is greater than n, and the line skip amount and the buffer offset amount are calculated based on the line feed ratio.
In a related aspect, the invention processes image data to be sent to a printer that prints image data on a recording medium at a print pixel resolution greater than a resolution of a print head and feeds the recording medium in units of a feed amount corresponding to (mxc3x971/n) pixels of the print head resolution, where m and n are integer numbers and m is greater than n, the image process comprising generating a line of image data, determining whether at least a number of contiguous lines of image data do not include a pixel to be printed, the number of contiguous lines corresponding to the feed amount unit, and sending line skip amount information to the printer based on a result of the determining step. The determining, step comprises storing the line of image data in a print buffer for transmission to the printer, and calculating the line skip amount. The determining step may further comprise calculating a buffer offset amount, and adjusting a starting position for storing the image data in the print buffer based on a result of the calculated buffer offset amount. The skip amount and the buffer offset amount are calculated in a case where a first line of image data to be stored in the print buffer is white data.
As a result of the foregoing, the invention controls a line feed amount and loading of image data in a print buffer to adjust for white image data encountered as at least the first line of the image data being loaded in the buffer. Therefore, the line feed ratio and line feed amount for advancing the recording medium to adjust for the white space is accommodated to provide for a faster line feed speed while at the same time controlling the data loading.
This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiment thereof in connection with the attached drawings.